1. Field of the Invention
This invention relates to an electronic circuit board case, particularly to a case for accommodating an electronic circuit board mounted with electronic components wherein resin is potted or charged into the space between the accommodated electronic circuit board and the inner wall of the case to immobilize and protect the electronic circuit board.
2. Description of the Related Art
An electronic circuit board mounted on a motorcycle or vehicle or the like must be protected from electronic component lead breakage and pattern exfoliation caused by shock and vibration imparted thereto from the exterior and also from corrosion and shortcircuiting defects caused by water immersion and moisture invasion. The electronic circuit board is therefore accommodated in a case and resin is potted or charged into the space between the electronic circuit board and the inner wall of the case to immobilize and protect the electronic circuit board.
FIG. 5 is a sectional view of a conventional electronic circuit board case.
A case 10 shown in FIG. 5, more specifically, a case main body 12 of the case, accommodates an electronic circuit board 16 inserted therein through an open end 14 at the top of the case. Connectors 18 and other electronic components are mounted on the electronic circuit board 16. (Electronic components other than the connectors 18 are omitted from the drawing.)
After accommodation of the electronic circuit board 16 has been completed, resin 20 is potted or charged into the space between the inner wall of the case main body 12 and the electronic circuit board 16. The resin 20 is potted or charged up to a level near the open end 14, more specifically up to a level where the cured resin 20 can retain (immobilize) and protect the electronic circuit board 16 and the connectors 18.
Further, Japanese Laid-open Patent Application No. Sho 62(1987)-95897, for example, teaches insertion of the electronic circuit board into the case after the case has been potted or charged with resin.
Since it is a property of the resin 20 to undergo a temporary decrease in viscosity during curing, the resin can penetrate even into the fine regions of the space between the case main body 12 and both the electronic circuit board 16 and electronic components. On the other hand, when the resin 20 is potted or charged to the foregoing level, it moves into the space between the case main body 12 and the connectors 18 owing to capillary action, overflows the open end 14 of the case main body 12, and runs out to the exterior.
This will be explained in further detail with reference to FIG. 6. Capillary action arising at a gap portion 22 between the case main body 12 and the connectors 18 causes the resin 20 to move toward the portions indicated by A and B in FIGS. 5, i.e., toward the portions where the case main body 12 and the connectors 18 are in contact (as indicated by the arrows in FIG. 6). The resin 20 then overflows the open end 14 in the vicinity of A and B and runs out to the exterior of the case 10.
The overflowing resin 20 sticks to the outside of the case main body 12 and spoils its appearance. Extra processing, such as a wiping step, has therefore been necessary.
Conventional practices for preventing outflow of the resin 20 include sealing the places where the resin 20 flows out by application of an adhesive or the like or potting or charging the resin 20 with the case 10 tilted about 15 degrees in the direction of the arrow in FIG. 5 so as to prevent potting or charging of resin into the portions that give rise to capillary action. Although these techniques are effective for preventing outflow of the resin 20, they do not help to prevent an increase in the number of fabrication steps.
On the other hand, when the electronic circuit board is inserted into the case after it has been potted or charged with resin, the resin is apt to overflow at the time of inserting the electronic circuit board.
When the case is used in an environment where it is exposed to shock and vibration, moreover, the strength of the case, particularly the strength of the open end thereof, is preferably increased. In addition, it is preferable to be able to retain (immobilize) the accommodated electronic circuit board and electronic components with high reliability.
Although Japanese Laid-open Patent Application Nos. Sho 62 (1987)-95897, Hei 10 (1998)-22312, Hei 8 (1996)-167455 and Hei 6 (1994)-243919, among others, teach techniques for resolving the foregoing issues, none solves them all.
An object of this invention is therefore to provide an electronic circuit board case that, without requiring any increase in number of fabrication steps, can prevent sticking of resin to the case exterior, is enhanced in strength, particularly the strength of the open end, and can reliably retain (immobilize) and protect an accommodated electronic circuit board and electronic components.
For realizing this object, a first aspect of this invention provides a case for an electronic circuit board mounted with electronic components, comprising: a case main body whose one end is opened; an opening formed at an outer periphery of the open end of the case main body; and retaining means for retaining the electronic circuit board inserted through the open end at a prescribed position in the case main body.
Since the case is formed with an opening at the outer periphery of the open end of the case main body and with the retaining means for retaining the electronic circuit board inserted through the open end at a prescribed position in the case main body, the electronic circuit board can be immobilized at the prescribed position in the case main body and the strength of the case (i.e. case main body), particularly the strength of the open end thereof, can be increased. Moreover, when resin is potted or charged into the case main body, any resin that runs out from the open end can be caused to flow into the opening.
In a second aspect, the present invention provides the case, wherein the opening is provided with a catcher such that resin potted in the case main body is caught by the catcher, when overflowing the open end.
Since the opening is provided with a catcher and any resin potted or charged into the case may body that overflows the open end and runs out to the exterior is caught by the catcher, the resin running out to the exterior of the case main body can be prevented from sticking to the outside of the case main body.
In a third aspect, the present invention provides the case, wherein a notch is formed at a portion of the open end where the case main body and a part of the electronic components are in close proximity with each other.
Since a notch is formed at a portion of the open end where the case main body and a part of the electronic components are in close proximity or in contact with each other, the space (gap) between the case main body and the electronic components concerned is enlarged. Since occurrence of capillary action is therefore inhibited, flow of resin to the exterior of the case main body is reduced.
In a fourth aspect, the present invention provides the case, wherein a rib is formed to interconnect the open end and the catcher across the opening.
Since a rib is formed to interconnect the open end and the catcher across the opening, the strength of the case (i.e., case main body), particularly the strength of the open end thereof, is further increased.
In a fifth aspect, the present invention provides the case, wherein the retaining means comprises at least the resin potted in the case main body, rails formed on an inner wall of the case main body, and a projection formed on a part of the electronic components to engage with a portion of the case main body close to the open end.
Since the retaining means comprises at least the resin potted or charged into the case, rails formed on an inner wall of the case main body, and a projection formed on some of the electronic components to engage with a portion of the case main body close to the open end, the electronic circuit board can be reliably introduced and immobilized at the prescribed position. Resistance of the electronic circuit board against shock and vibration imparted from the exterior is therefore enhanced.
In the sixth aspect, the present invention provides the case, wherein the case main body is formed to have an irregular profile matched to the shape of the electronic components.
Since the case main body is formed to have an irregular profile matched to the shape of the electronic components, the volume of the case (i.e. case main body) can be made small and the amount of potted or charged resin reduced.